September and October for UK Rapeseed growers has proven to be the most challenging of times over the last decade as Cabbage Stem flea beetle numbers make production of the crop almost unviable due the havoc and damage the beetles can do to newly emerging plants.
There are numerous accounts across the UK where flea beetle has wiped our crops to the point whereby the crop is completely wiped out and so many growers walked away from even trying to produce it even though demand increases.
10 years ago, Engage created the technology Sentinel, originally to aid production of wound tissue in regularly harvested crops to reduce infection points for diseases entry. However, over the past five years it has developed a strong following in many crops for its ability to dissuade insect from predating.
This ability extends from slugs and snails, to aphids, thrips and even more hardier pests including Flea beetle.
So how is Sentinel helping Oilseed rape farmers?
Sentinel is a unique blend of stabilised silicic acid (pure available nutrient silicon) and salicylic acid which stimulate growth and natural process within crops to protect them from predation.
How it works?
Sentinel works in three ways:
- Natural strength increase
- Increased protective growth mechanisms
- As a strong negative feeding deterrent
Silicon and Predation
Mechanisms and Benefits of Silicon Application
Pest Resistance: The primary reason growers use silicon is to combat the cabbage stem flea beetle (CSFB) and slugs. The high levels of available silicon in Sentinel stimulates leaf hair (trichome) production in oilseed rape (Brassica napus) and many other commercially grown crops.
Commercial field trials and agricultural data demonstrate that applying silicon to oilseed rape increases leaf hair length, density, and strength. Also dicotyledonous crops do not accumulate silicon like monocots (such as cereals and grasses) can, so use it to support cellular growth and to reinforce structural integrity in the plant and in the cuticle layer. The cuticle layer increases in thickness and leaf wax production increases.
The increased density of leaf hairs, combined with the leaf producing greater leaf wax which combined with silicon becomes a hard glass-like crystal layer of “opals” (phytoliths) within the leaf cuticle, creating a highly effective mechanical barrier. This makes the leaves physically abrasive, difficult to navigate and unappealing for pests to chew on.
Water Management and Climate Resilience: Increased leaf hair production assists in transpiration management, which reduces water loss. Silicon additionally modifies root cell wall structures to protect the plant against drought stress and water deficiency.
Structural Integrity: Beyond leaf hairs, silicon acts as a “cellular cement,” thickening the cuticle tissue and strengthening the plant stems to support higher leaf, flower, and overall crop yields.
Also, Silicon creates a negative feeding response in insect pests through a combination of physical, chemical, and digestive barriers. When an insect attempts to feed on a silicon-rich leaf, it experiences a highly unpalatable and physically damaging environment.
The primary mechanisms behind this negative feeding response include:
Mouthpart Wear and Damage
- Abrasive Phytoliths: Absorbed silicon is deposited within and between the plant’s cell walls as microscopic, glass-like crystals called biogenic opals or phytoliths.
- Mandibular Wear: For chewing insects (like beetles or caterpillars), chewing these microscopic glass structures causes irreversible wear and tear to their mandibles (mouthparts). As their mouthparts blunt, their ability to feed decreases drastically, leading to starvation or abandonment of the plant.
Physical Epidermal Toughness
- Cell Wall Armour: Silicon forms a rigid “silicon–cuticle double layer” just beneath the leaf surface.
- Penetration Resistance: This acts as a physical shield that makes the tissue highly resistant to tearing, puncturing, or boring. Insects find it physically exhausting to chew through the toughened epidermis, which discourages prolonged feeding.
Reduced Digestibility and Gut Damage
- Low Nutritional Value: Silicon reduces the overall palatability and digestibility of the leaf matter.
- Internal Lacerations: When insects do manage to ingest pieces of a silicified leaf, the sharp phytoliths and rigid leaf hairs (trichomes) can cause physical lacerations to the insect’s gut. This alters their metabolism, stunts their growth, and reduces their reproductive capacity.
Upregulated Chemical Defences
- Hormonal Alert Systems: Silicon accumulation interacts directly with the plant’s jasmonic acid (JA) pathway, which regulates stress and defence hormones.
- Secondary Metabolites: When an insect bites the leaf, the presence of silicon triggers a faster, more intense surge of defensive chemicals (like toxic secondary metabolites and anti-nutritional enzymes) that make the plant taste bitter or toxic.
Altered Volatile Signals (The “SOS” Call)
- Attracting Predators: Silicon changes the natural chemical composition of the Herbivore-Induced Plant Volatiles (HIPVs)—the scents a leaf releases when wounded.
- Biological Warfare: These modified airborne compounds act as a distress signal, actively recruiting natural predators and parasitic wasps to the area to attack the feeding insects.
Salicylic Acid
Salicylic acid (SA) is a crucial phytohormone that acts as a master regulator for a plant’s growth, survival, and stress management. Beyond deterring insect pests, it plays vital roles in environmental adaptation and developmental processes.
Boosting Abiotic Stress Tolerance
SA is a powerful antioxidant manager that helps plants survive harsh environmental conditions by mitigating cellular oxidative damage:
- Drought and Salinity: It regulates stomatal closure to prevent water loss and maintains the osmotic balance in roots during high-salt conditions.
- Extreme Temperatures: SA stabilizes cell membranes during heat and chilling stress, preventing the breakdown of vital proteins.
- Heavy Metal Toxicity: It prevents plants from absorbing dangerous levels of metals like cadmium, lead, or aluminium from the soil.
Regulating Photosynthesis and Growth
- Chlorophyll Protection: SA maintains optimal chlorophyll levels and protects the photosynthetic machinery (specifically Photosystem II) from degradation under intense sunlight.
- Stomatal Regulation: By controlling the opening and closing of stomata, SA fine-tunes the balance between carbon dioxide uptake and water conservation.
Importantly within Sentinel the blend of both Silicon and salicylic acid triggers the production of Salicin
Salicin is a bitter-tasting phenolic glycoside found naturally in the leaves of many plants and trees. Unlike the mechanical armour provided by silicon, salicin acts as a chemical deterrent.
Salicin creates a negative feeding response in generalist insect pests through a combination of taste deterrence, and digestive disruption:
Intense Bitter Taste (Feeding Deterrence)
- Aversive Flavour: Salicin is highly bitter. Most generalist insects possess specialized gustatory receptors (taste receptors) on their mouthparts that detect bitter deterrents.
- Immediate Rejection: Upon taking an exploratory bite, the high concentration of salicin triggers a strong rejection response, prompting the insect to stop feeding immediately and migrate away from the plant.
Conversion to Gut Toxins
- Enzymatic Degradation: When an insect masticates and swallows a salicinoid-rich leaf, the chewing action and the insect’s own digestive enzymes hydrolyse in to complex salicin compounds which are very difficult to digest and reduce the feeding ability of the Flea beetle if it continues to feed.
All the above nutritionally stimulated responses result in an effective feeding deterrent and is proven in both trials and four years of commercial use.
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